By definition, a polynomial's degree is the highest or the greatest power of a variable in a polynomial equation.
We have the following polynomial
![P(x,y)=x^4-3x^2+2y-1](https://img.qammunity.org/2023/formulas/mathematics/college/gh7uublzfhceuiy1u3q7dyyb8cpl9765o8.png)
The first term has the greatest power, and it is 4(it is x to the 4th power).
Then, by definition, this polynomial is a polynomial of degree 4.